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Posted to commits@pinot.apache.org by "walterddr (via GitHub)" <gi...@apache.org> on 2023/11/16 17:16:43 UTC
[I] [multistage][feature] revisit RelDistribution detection logic [pinot]
walterddr opened a new issue, #12012:
URL: https://github.com/apache/pinot/issues/12012
This discussion stems from: #11976
Status quo
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we currently
1. explicitly insert *logical* exchanges where we *might* require data shuffling; and
2. then determine whether those exchanges are real data shuffle or possible passthrough;
3. then we determine whether to assign more/less servers to run either side of the exchanges
Current solution
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This PR only addresses step-2: to give it a better idea on whether the RelDistribution is the same before & after an exchange. for this purpose, it is OK (at this point) to only keep one of the 2 sides for JOIN Rel.
Needs revisit
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there are several problems
1. should we explicitly insert exchange or should we use other abstractions?
- there are other ways to add exchange nodes that are more "Calcite-suggested" when managing the Exchange insert instead of applying them during optimization IMO.
2. should the exchange insert be RelDistribution-based or physical-based?
- we are mixing the concept of Exchange usage: it can mean (1) altering logical RelDistribution, (2) indicating there potentially could be physical layout differences, (3) whether we can apply leaf-stage optimization
- although (3) will be addressed by #11937, we should consider whether to still use ExchangeNode as our abstraction or create our own to avoid confusion
3. should we apply RelDistribution trait before or after Exchange insert
- currently we have to do this after insert, but technically if we addresses question (2) we can potentially apply that beforehand
ultimately utilizing Exchange was a quick decision during early stage multi-stage engine development and it might not have been the best option. it is worth taking some time to revisit
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Re: [I] [multistage][feature] revisit RelDistribution detection logic [pinot]
Posted by "walterddr (via GitHub)" <gi...@apache.org>.
walterddr commented on issue #12012:
URL: https://github.com/apache/pinot/issues/12012#issuecomment-1814891976
CC @xiangfu0 @Jackie-Jiang @ankitsultana
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